Arrangement for the sparkless interruption of currents



Aug. 18, 19420 J. JONAS 2,293,296

ARRANGEMET FOR THE SPARKLESS INTERRUPTION OF CURRENTS Filed Jan. ,8;1941 3 Sheets-Sheet l ARRANGEMENT FOR THE SPARKLSS INTERRUPTION OFCURRENTS Filed Jan. 85.1941 5 Sheets-Sheev'; 2

Patented Aug. 18, 1942 u ABRANGEMENT FOR THE SPARKLESS INTERRUPTION OFCURRENTS Julius Jonas, Zurich, Switzerland, assigner teAktiengesellschaft Brown,

Baden, Switzerland Boveri & Cie.,

Application January 8, 1941, Serial No. 373,701

` In Switzerland July 28, 1939 17 Claims. (Cl. 175-364) It is oftenrequired that circuits in which very high currents are flowing should beinterrupted by means of a mechanical switch. Various proposals have beenmade in order to prevent sparking or arcing occurring when the currentis interrupted, but in practice these known means have not been found tobe satisfactory. It has for instance been proposed that a reactor.already saturated at very low currents, should be arranged in serieswith the switch contact. By this means the current curve when passingthrough zero becomes flattened so that the switch has only to interrupta small current. It is also known to connect condensers in parallel withthe switch. These devices enable a certain. improvement to be achieved;they are, however, very expensive and cannot prevent sparking duringcommutation and the subsequent destruction of the switch contacts. whileat the most they can only prolong the life of the contacts.

According to the invention a sparkless operation of a mechanicallyactuated switch is also achieved :for very high currents by connecting arectifier in parallel with the switch and an auxiliary source of voltagein series with the rectier, the voltage from the auxiliary source beingarranged to be positive with reference to the passage of current throughthe rectifier at least during the opening period of the switch and ofsuch a magnitude that it at least equals the voltage at which therectier becomes operative.

The objects and advantages of the invention will be apparent from thefollowing specification when taken with the accompanying drawings, inwhich:

Fig. 1 is a diagrammatic representation of a single-phase arrangementaccording to the invention;

Figs. 2a to 2c are curve sheets showing the method of operation of thearrangement of Fig. l;

Fig. 3 is a diagrammatic representation oi the three-phase arrangementaccording to the invention; 4 Fig. 3a shows the voltage curve and Fig.3b

the current curve for each phase;

Fig. 4 shows further details of a three-phase arrangement as regards thecontrol of the auxiliary rectifier;

Figs. 5 and 6 show modified forms of the invention as applied tothree-phase arrangements employing a single auxiliary rectiiier forA allphases.

which supplies the load V over the switch S. In parallel with the switchS is arranged a rectiiler G and in series with this latter the auxiliaryvoltage source En. As shown in the drawings this auxiliary rectiiler Gpreferably consists of a gas or vapor discharge vessel which is providedwith a preignition device so that the rectifier has a definite operatingor ignition voltage Ez and for instance an approximately equally highvoltage drop when in operation. The magnitude and phase of the auxiliaryvoltage Ez when compared with the ignition voltage, the primary supplyvoltage E1 and the phase, at which the switch S for instanceperiodically interrupts the circuit, shows the difference between thevarious cases. In Figs. 2a, 2b and 2c it is assumed that the phase ofthe auxiliary voltage E2 lags 60 behind fler about corresponds to thevoltage peak indicated above the ignition voltage line Ez. Soon afterthe switch is opened the current therein drops to zero, whileimmediately afterwards there is a current J2 owing through the rectifierin the same sense and which also sinks to zero` before the voltage E1passes through zero value. The current Jz thus augments the interruptedcurrent J1 of the load V, so that during the opening of the switch anapproximately sinusoidal current flows through the alternating voltagesource E1 and through the load V and thus effectively suppresses thehigh induced voltages and the resulting sparking and arcing in themechanical switch S. If the voltage E2 is selected to equal the ignitionvoltage Ez as indicated in Fig. 2b, fundamentally the same effect isobtained but with the difference, however, that the current J2 lastssomewhat longer. If the voltage E2 is bigger than 'the voltage Ez (Fig.2c) then there is no longer a sudden fall in J1 and a momentary rise inJ2, but rather a continuous current transfer from the switch to theauxiliary rectiiier. Such an interrupted current transfer isparticularly favorable in the case of threephase systems in order to beable to obtain good commutation between the phases.

The three-phase arrangement shown in Fis. 3

In Fig. 1 E1 is the alternating voltage source 55 deals with a system oiconnections which is preferably used when a low voltage rectifier forvery high currents is required. The delta connected primary winding P ofa transformer T is supplied from the network N, the secondary winding Qof the transformer comprising two parts, each of which serves a diierentpurpose. The three switch contacts U1, U11, Um are directly connected tothe star-connected phase windings which are dimensioned for the maincurrent and generate the voltages I, II, III. In series with thestarconnected main winding is an auxiliary winding with the phasevoltagesI', II', III' which supply the three anodes Ai, An, Ain of therectier G. The entire secondary winding forms a zig-zag connection sothat the auxiliary voltages with iridices lag by 60 behind the voltageswithout indices at the switch H. The common cathode K of the threedischarge gaps in the auxiliary rectier G is connected with the rotatingswitch arm H to which also one terminal of the load V is connected.rI'he other terminal of the load V is connected to the neutral point Oof the secondary winding Q of the transformer T. The switch H is drivenby a synchronous motor not shown in the drawing and also preferablyconnected to the transformer T in such a manner that one period ofrotation is exactly equal to the period of the alternating current inthe network N. Electric lters for smoothing the direct current can alsobe arranged in series with the load V. In order to render thecommutation, explained with reference to Fig. 1, as far as possibleindependent of the load, a regulating reactor can also be connected inseries with the cathode of the rectier G, this reactor being controlledby a direct current transformer in series with the load V. With a largesupply current the inductance of this reactor must be small in order toensure that there is a large increase in the commutation current takenover by the rectier and'corresponding to the main current. On the otherhand with a small supply current it is desirable, for the sake ofeconomy, that the current flowing through the rectifier should beproportionately smaller. This can be readily achieved' by increasing theinductance of.the series reactor. An automatic regulation is, however,preferable. Such an auxiliary dev ice is indicated in the arrangementshown in Fig. l by means of dotted lines, F being the directcurrent-transformer and R the regulating reactor controlled by theformer. This device can of course also be used with the arrangementillustrated in Fig. 3 and has only been omitted from the drawing for thesake of clearness. is also provided with a pre-igniter similar to thatin Fig. 1. The curves for the voltages E of the three-phase arrangementare shown in Fig. 3a and the corresponding current curves J areindicated in Fig. 3b. In both figures the contact duration of themechanical switch or commutatorv is indicated by the double lines drawnparallel to the time axis, and for instance H Uii indicates that thecontact arm H remains connected to the contact segment Un during thisperiod of time. The

curves I, II, III in Fig. 3a show the course of the voltage for eachphase of the main winding, while the curves I', II', III represent thevoltage for each phase of the auxiliary winding of the transformer T.The voltage on the anodes A1, An, Ani

The cathode K of the rectifier G in Fig. 3 i' in Fig. 3b by Ji, Jn, Jin,and the current taken by the various discharge gaps is indicated by J g.In connection with the current and voltage curves shown it is assumedthat the load V is mainly ohmic.

For capacity or inductive loads and also for the purpose of theaforementioned automatic regulation of the commutation current taken bythe auxiliary rectifier it is often an advantage when the anodes of therectifier are controlled by known means so that the moment at whichignition occurs can be selected as desired. For this purpose a magnetoignition apparatus B, as shown in Fig. 4, can be coupled with the switchH for supplying the ignition impulses required for such a regulation. Itis preferable if the anodes are controlled by means of a directapplication of the spark to the anodes. The apparatus B should thus beconnected to the anodes over spark gaps C. The ignition apparatus B can,however, also be used to impose voltage impulses on grids arranged infront of the anodes, whereby the moment when the rectifier is ignited iscontrolled in the desired manner, for instance in dependence on the loadon the main current. The sparkless commutation of the current which canthus always be obtained, makes the arrangement according to theinvention particularly suitable for rectifier plants in which with ahigh overall efficiency Very small direct voltages and high currents areto be produced. In the first place therefore this refers toinstallations in which the usual rectier entirely composed of dischargevessels would provide too poor an efficiency due to the inherent voltagedrop of between 15 and 25 volts. Since the main current ows overmechanically operated contacts and the rectier only serves i orcommutation purposes and is therefore only designed for a correspondingfraction of the output, the weight and space required by this newmechanical rectifier whenreferred to the total output will becomparatively favorable and is within the usual limits even at very lowvoltage.

The present invention also deals with further improvements in themechanical rectiers with synchronously controlled contacts alreadyreferred to, and in which the current commutation is dealt with by meansof an auxiliary rectifier having an additional voltage connected inseries, mercury vapor rectifiers being preferably used for this purpose.The auxiliary rectifiers used hitherto for multi-phase operation areprovided with an anode for each phase so that each individual anode hasin turn to commutate the full current. The auxiliary rectifier is thussimilar to a standard rectier designed for full current and full voltageand this increases the cost of the installation very considerably. It istherefore also an object of the invention to simplify and cheapen theauxiliary rectier and at the same time also to obtain more favorableoperating conditions for the mechanical contact device or commutatorthus enabling also its coristruction to be simplified.

In the constructional examples of the invention shown diagrammaticallyin Figs. 5 and 6 the auxiliary tube or rectier G has to relieve thecontact device S during commutation, that is when current passes fromone phase to the next. The rectifier G is therefore current conductiveonly during very short intervals of time. When the commutation processis properly carried out the individual phases do not overlap and it isthus possible to employ only one singleanode auxiliary rectier tube G ifthis latter is always switched over early enough to the commutatingphase by means of an auxiliary contact device Sz. This auxiliary contactdevice or commutator must have the same number oi phases as the maincontact device S and be controlled in synchronism with this latter, thecontact periods being adjusted to suit the commutating conditions. 'I'heauxiliary commutator Sz closes and opens its contacts without currentflowing when the commutation process is controlled accordingly and needonly be dimensioned for a relatively small eifective current value owingto the short time during which current conduction takes place. Thereduction in Vthe number of anodes from for instance six to one in asix-phase rectifier and therefore the corresponding reduction in size ofthe auxiliary rectifier G results in the following advantages: Themaximum negative blocking voltage for the auxiliary rectiiier tube canbe reduced if it is switched oil' as soon as commutation has iinishedbefore the blocking voltage reaches its maximum value, and is onlyswitched in again shortly before the beginning of the commutation whenthe blocking voltage has passed its maximum value. The single-anode tubehas also the advantage when compared with a multiphase rectiier thatduring the non-conductive period there is no current conducting mainanode in the tube which increases the back-arcing tendency of therectifier. The auxiliary rectifier can therefore be considerablysimplified because the usual elements such as the anode grids andshields can be omitted. An important simplitlcation is also achieved inconnection with the simultaneous reduction in voltage drop. Dischargetubes with mercury vapor filling can be used in which the arc isreignited for each current conducting period. 'Ihe reduction in arcvoltagev in the auxiliary rectiiier is not only of importance as regardseillciency but is also l important in connection with the magnitude ofthe auxiliary voltage and the stressing of the main contacts when theswitch is opened.

The cost of such a mechanical rectiiier with an auxiliary discharge tubecan .be further reduced if the commutating power is decreased becausethis latter directly determines the capacity of the auxiliary rectifierand the auxiliary commutating device. In arrangements having a pluralityof phases this can be achieved by subaaforementioned measures it ispossible reduce the auxiliary rectifier to one-tenth its former dividingthe system into several multi-phase systems which are connected inparallel by means of absorption coils; for instance a six-phase systemcan be divided into two three-phase systems with a double-limbedabsorption coil or into three two-phase systems with a triple-limbedabsorption coil. These systems have, in addition to the advantagealready known in connection with rectifier systems, also the valuableproperty that the power of the commutating device is also reduced inproportion to the number of systems operating in parallel, that is 1:2or 1:3. This is due to the fact that the entire direct current in theabsorption coil connections distributes itself simultaneously overseveral phases while only one phase and therefore only a fraction of thethe main mechanical commutating device is also relieved by a reductionin the maximum and eective value of the current which it has to conduct.By a simultaneous application of thesize so that quite apart from theother advantages which result, the supplementary cost for thecomparatively small auxiliary contact device is practically negligible.

In seriesy with the auxiliary rectiner or discharge tube is an auxiliaryvoltage source which initiates the ignition and current ilow in theauxiliary rectiner. This auxiliary voltage E: is a three-phase one forthe arrangement shown in Fig. 5. It is, however, also possible to -use asingle-phase voltage En which as indicated in Fig. 6 is arranged to bein series with the cathode of the single or multi-phase tube G. Thefrequency of this auxiliary voltage Ez must, however, be higher thanthat of the line frequency and depends upon the number of commutationsoccurring during each cycle. For a six-phase rectifier it will thereforebe necessary to employ a voltage having a frequency o! 300 cycles. The

scribed. 'I'he plant is also considerably simplified when a single-phaseauxiliary voltage with a` high frequency is employed. Furtherpossibilities for simplifying the commutation process and adjusting itto suit varying operating and load conditions are provided by regulatingthe phase and amplitude of the voltage. The auxiliary rectiiier G can ofcourse also be equipped with means for influencing the point ofignition. 'Ihese means can also be used in order to switch in theauxiliary commutator without sparking.

I claim:

l. Arrangement for the sparkless interruption of alternating current in'a circuit containing a periodically actuatedmechanical switch,comprising a rectifier in parallel to the switch, and an auxiliarysource of alternating voltage in series with the rectifier, saidauxiliary source being adapted to supply a voltage displaced in phasefrom the voltage of the principal circuit so that the maximum amplitudeof the half wave of the auxiliary voltage which is positive with respectfo the ilow of current in the rectifier substantially coincides with theopening of the switch and is at least approximately equal to thevoltperiodically actuated switch in each phase, a rectifier in parallelto the switch, and an auxiliary source of alternating voltage in serieswith the rectiiier, said auxiliary source being adapted to supply avoltage displaced in phase from the voltage of the principal circuit sothat the maximum amplitude of the half wave of the auxiliary voltagewhich is positive with respect to the now of current in the rectifiersubstantially coincides with the opening of the switch and is at leastapproximately equal to the voltage at which the rectier becomesoperative.

5. Arrangement as claimed in claim 4 wherein the supply voltage and alsothe auxiliary voltage are obtained from a star-connected zig-zagsecondary winding of a three-phase transformer,

=those phase parts of the secondary winding which lie directly at theneutral point providing the supply voltages and those phase parts oi thesecondary winding which have a lag of 60 pro- `viding the auxiliaryvoltages.

6. Arrangement as claimed in claim 4 including a rectifier which isassociated with the various phases consisting ofa number of dischargecells arranged in a common housing and having a common cathode.

7. Arrangement as claimed in claim 4 including a rectiiier which isassociated with the various phases consisting of a number oi.' dischargecells arranged in a common housing and having a common cathode andprovided with a special source of electrons.

8. Arrangement as claimed in claim 4 including a rectifier which isassociated with the various phases consisting of a number of dischargecells arranged in a common housing and having a common cathode andprovided with means for controlling the time cf ignition.

9. Arrangement for the sparkless interruption of multiphase alternatingcurrent comprising a synchronously operated multiphase switch, arectiiier in parallel to the switch, and an auxiliary source ofalternating voltage in series with the rectifier, said auxiliary sourcebeing adapted to supply a voltage displaced in phase from the voltage ofthe principal circuit so that the maximum amplitude of the half wave ofihe auxiliary voltage which is positive with respect to the iiow ofcurrent in the rectifier substantially coincides with the opening of theswitch and is at least approximately equal to the voltage at which therectiiier becomes operative, the. rectiiier which is associated with thevarious phases consisting of a number of discharge cells arranged in acommon housing and having a common cathode, and a magneto ignitionapparatus coupled with said switch to control the ignition of therectifier.

10. Arrangement for the sparkless interruption of multiphase alternatingcurrent comprising a synchronously operated multiphase switch, arectifier in parallel to the switch, and an auxiliary source ofalternating voltage in series with the rectiiier, said auxiliary sourcebeing adapted to supply a voltage displaced in phase from the voltage ofthe principal circuit so that the maximum amplitude of the haii wave ofthe auxiliary ical rectier is switched over to the commutating phase asrequired.

12. Arrangement as claimed in claim 4 wherein the auxiliary rectiiierconsists of a singlephase auxiliary discharge tube which by means of anauxiliary commutating device operated synchronously with the contacts ofthe mechanical rectiner is switched over tothe commutating phase asrequired, and the auxiliary commutating device rapidly disconnects theauxiliary rectifier during periods which fall outside the periodrequired for commutation so that said auxiliary rectiiier does notrequire a maximum blocking voltage.

13. Arrangement as claimed in claim 4 wherein the auxiliary rectinerconsists of a singlephase auxiliary discharge tube which by means of anauxiliary commutating device operated synchronously with the contacts ofthe mechanical vrectiner is switched over to the commutating V-phase'asrequired, and multi-phase connections with absorption coils are employedin order to reduce the size of the commutating device and the load whichthe contact device has to carry. 14. Arrangement as claimed in claim 4wherein the auxiliary rectier consists of a singlephase auxiliarydischarge tube which by means voltage which is positive with respect tothe iiow of current in the rectier substantially coincides with theopening of the switch and is at least approximately equal to the voltageat which the rectier becomes operative, the rectier which is associatedwith the various phases consisting of a number of discharge cellsarranged in -a common housing and having a common cathode, and a magnetoignition apparatus coupled with said switch to control the ignition ofthe rectier in dependence on the loading,

of the principal current circuit.

11. Arrangement as claimed in claim 4 wherein the auxiliary rectiiierconsists of a singlephase auxiliary discharge tube which by means of anauxiliary commutating device operated synchronously with the contacts ofthe mechanof an auxiliary commutating device operated synchronously withthe contacts oi' the mechanical rectiiier is switched over to thecommutating phase as required, and the commutation voltage consists ofan auxiliary voltage source of higher frequency, said voltage sourcebeing connected in series with the auxiliary rectifier.

15. Arrangement as claimed in claim 4, wherein the auxiliary rectifierconsists of a singlephase auxiliary discharge tube which by means of anauxiliary commutating device operated synchronously with the contacts ofthe mechanical rectiiier is switched over to the commutating phase asrequired, and the commutation voltage consists of an auxiliary voltagesource of higher frequency, said voltage source being connected inseries with the auxiliary rectifier and the phase of the commutationvoltage being variable in accordance with operating conditions.

16. Arrangement as claimed in claim 4 wherein the auxiliary rectierconsists of a singlephase auxiliary discharge tube which by means of anauxiliary commutating device operated synchronously with the contacts ofthe mechanical rectier is switched over tc the commutating phase asrequired, and the commutation voltage consistsof an auxiliary voltagesource of higher frequency, said voltage source being connected inseries with the auxiliary rectiiier and the amplitude of the commutationvoltage being variable in accordance with operating conditions. 17.Arrangement as claimed in-claim 4 wherein the auxiliary rectier consistsof a singlephase auxiliary discharge tube which by means of an auxiliarycommutating device operated synchronously with the contacts of themechanical rectiiier is switched over to the commutating phase asrequired, and the main commutation device is so regulated that theauxiliary commutating devicecan be switched from phase to phase Withoutsparking.

JULIUS JONAS.

